Infant M. nemestrina monkeys, when separated from their mothers, generally exhibit a period of agitation, followed by a depressive reaction of varying severity and duration. We believe this depressive reaction to be the best available animal model of human depression. Working with support of Grant no. MH 19514 we have developed the telemetry technology necessary to study multivariable physiology (heart rate, body temperature, EOG, EMG, 3 channels of EEG) simultaneously with behavior in the monkey infant unrestrained in the social group, or surrogate-reared. We are studying 18 infants under a variety of experimental conditions to further document the nature and variability of the physiological response to separation, with special emphasis on depression, and develop a Biobehavioral Developmental Profile for the monkey infant that will permit each infant to be assessed along a spectrum of developmental indices both physiological and behavioral. Physiological parameters include circadian and ultradian rhythms (body temperature, heart rate, sleep stage), heart rate and EEG correlates of behavior, development of EEG rhythms (alpha, lambda, sensorimotor, and sleep rhythms), and the physiological responses to stress. The possible roles of altered nutrition or loss of maternal body heat in the physiological response to separation will be specifically tested. We believe this combined physiological-behavioral research on the monkey infant will expand its usefulness to psychiatry and the behavioral sciences as an animal model of (1) affective disorders, specifically depression, (2) possibly psychosomatic disorders, (3) neurochemical contributions to the processes manifested, and (4) normal psychobiological development. BIBLIOGRAPHIC REFERENCES: Reite, M., Stynes, A.J., Vaughn, L., Pauley, J.D., Short, R. Sleep in infant monkeys: normal values and behavioral correlates. Physiol. and Behav. 16:245-251, 1976. Reite, M., Pauley, J. D. Multichannel implantable biotelemetry: Problems, Pitfalls, and Rewards. Proceedings of the 3rd International Symposium on Biotelemetry, Asilomar, California, 1976. Abstract in Biotelemetry 3: 21, 1976.